The present invention relates to safe and compact storage for storing ammonia a method for producing a compact storage for storing ammonia, systems comprising a compact storage for delivery of ammonia to ammonia consuming units and use
1. Field of the Invention
The present invention relates generally to the use of using solids for reversible storage of ammonia in solid form. In the solid form, ammonia can be transported safely, efficiently and can be released by thermal desorption and used in various applications such as fuel cells and in controlled delivery in selective catalytic reduction of NOx using ammonia as reducing agent.
Transporting ammonia as a pressurized liquid is hazardous if the container bursts caused by an accident or if a valve or tube breaks. In the case of using a solid storage medium, the safety issues are much less critical since a small amount of heat is required to release the ammonia and the equilibrium pressure at room temperature can be—if a proper solid material is chosen—well below 1 bar.
The invention relates to the storing ammonia in solids for the purpose of ammonia storage, transport and delivery to stationary and mobile applications such as catalytic removal of NOx (selective catalytic reduction using ammonia).
The present invention is especially suitable as a source for providing ammonia in selective catalytic reduction in exhaust gasses for reduction of emission from stationary and mobile combustion engines or power plants fuelled by methanol, ethanol, hydrogen, methane, ethane or any other synthetic fuel. Mobile combustion engines for which the invention is suitable are may e.g. be automobiles, trucks, trains, ships or any other motorised vehicle. The invention is particularly suitable for use in connection with reduction of NOx in combustion gases from automobiles and trucks.
Stationary power plants for which the invention is suitable are preferably power plants generating electricity.
Furthermore, the solid ammonia storage material can be used as energy carrier applied in the field of fuel cell technology. Ammonia can be catalytically decomposed into N2 and H2 for the use in PEM fuel cells and alkaline fuel cells or directly as ammonia in SOFC's (Solis Oxide Fuel Cells) and alkaline fuel cells. With a high ammonia storage density, the energy required to desorb and decompose ammonia still makes it a well-suited candidate for indirect hydrogen storage.
The critical part of preparing a useful solid ammonia storage medium is to obtain sufficiently high ammonia content—in particular with respect to the amount of ammonia per unit volume of the storage medium. This can be related to the demands from DOE (US Department of Energy) for hydrogen storage. Efficient ammonia storage can just as well be considered as an efficient hydrogen storage material due to the high hydrogen content in NH3.
2. Description of the Related Art
In published international application No. WO 90/10491 is disclosed control of volumetric expansion of e.g. ammonia complexes of salts during adsorption and desorption in order to maintain heat transfer and reaction rates. This is obtained by compression by means of an outer barrier limiting the volumetric expansion during chemisorption.
Published US patent application No. US 2001/0053342 discloses a method for selective NOx reduction in oxygen-containing exhaust gases using ammonia and a reduction catalyst according to which gaseous ammonia is made available by heating a solid storage medium in a container.
US 2001/0053342 is silent with respect to compacting of the solid storage medium.